RoomAdapter.kt

class RoomAdapter(val championId: String) : RecyclerView.Adapter<RoomViewHolder>() {

    private var messages = mutableListOf<Message>()

    fun addMessage(message: Message) {
        messages.add(message)
        notifyItemChanged(messages.size - 1)
    }

    override fun onCreateViewHolder(parent: ViewGroup, layoutResource: Int): RoomViewHolder =
            RoomViewHolder.create(parent)

    override fun getItemCount(): Int = messages.size

    override fun onBindViewHolder(holder: RoomViewHolder, position: Int) =
            holder.bind(messages[position], championId)
}